The present invention relates to a process for regenerating a spent molecular sieve catalysts of the Fluidized Catalytic Cracking Unit (FCCU) in oil refinery. More particularly, the present invention relates to a process for regenerating a spent molecular sieve catalysts using two riser regenerators.
Up till now, the molecular sieve catalyst, which has been used in FCCU, is regenerated in a fluidized bed and a combustion riser. The combustion riser is not used alone, and must be used in combination with a fluidized bed. But, the fluidized bed regeneration has the following problems: long catalyst residence time, serious catalyst back-mixing, low Carbon Burning Intensity (CBI), complicated inside structures, difficult to uniformly fluidize and keep a good distribution of particles, easy damage of the inside equipment, etc.
In recent years, the riser regenerator has received substantial interest. But, coke combustion in the riser regenerator requires circulation of a high temperature catalyst and air injection at various heights of the riser regenerator, and back-mixed problem has not been solved. It is not able that main operation parameters such as space-velocity and temperature are both high at the same time.
Accordingly, it is an object of the present invention to provide a process of regenerating spent molecular sieve catalysts comprising the steps of:
(1) mixing a high temperature flue gas that comes from a second group of cyclones with the spent catalyst in a first riser regenerator to form a mixture of a half-regenerated catalyst and a flue gas at the top of the first riser regenerator;
(2) separating the half-regenerated catalyst from the mixture in a first group of cyclones;
(3) mixing the half-regenerated catalyst that comes from the first group of cyclones with a sufficient amount of air for burning off all coke on the spent catalyst in a second riser regenerator to form a mixture of a high temperature flue gas and a regenerated catalyst at the top of the second riser regenerator;
(4) separating the regenerated catalyst from the mixture in the second group of cyclones; and
(5) recovering surplus heat from the regenerated catalyst that comes from the second group of cyclones by a regenerated catalyst cooler which is located outside of the second riser regenerator.